Vacancy-Type Defects Study on Ultra-Fine Grained Aluminium Processed by Severe Plastic Deformation
Vacancy-type defects play an important role in the metal materials deformed by severe plastic deformation (SPD). The present work use positron annihilation lifetime spectroscopy (PALS) to test the vacancy-type defects in aluminium alloys processed by equal channel angular pressing (ECAP) and accumulative roll bonding (ARB). ECAP at room temperature (RT-ECAP) and cryogenic temperature (CT-ECAP) was conducted to AA1050 and ARB with 200 °C pre-heating was conducted to AA1050 and AA6061 to produce laminated AA1050 sheets, AA6061 sheets and AA1050/AA6061 composites. High fraction of vacancy-type defects were detected in all the deformed samples. Vacancies associated with dislocations and bulk mono-vacancies have been identified in RT-ECAP deformed samples. Three types of vacancy-type defects, vacancies associated with dislocations, bulk mono-vacancies and bulk di-vacancies, have been identified in the CT-ECAP processed samples. The ARB process is more efficient in grain refinement and strengthening. However, the accumulation of vacancy-type defects in ARB deformation seems less efficient. Vacancies associated with dislocations are the major vacancy-type defects for ARB processed AA1050 sheets but there exist some bulk mono-vacancies. However, most of the vacancy-type defects in the ARB processed AA6061 are vacancies associated with dislocations. A very small fraction of bulk mono-vacancies can be extracted but it is so small that it can be neglected. The lifetimes of ARB processed AA1050/AA6061 composites are generally in between the values of AA1050 sheets and AA6061 sheets. Voids were not detected in neither of the samples.
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Document Type: Research Article
Publication date: July 1, 2014
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